Method of combustion for low-grade fuel and apparatus therefor



Jan. 12, 1960 I T. TINKER 2,920,689

urn-x00 0F coususnou FOR LOW-GRADE FUEL AND APPARATUS THEREFOR Filed Kay15. 1952 2 Sheets-Sheet. 1

' mmvron. J Om 'r. TINKER METHOD OF COMBUSTION FOR LOW-GRADE Jan. 12,1960 FUEL AND APPARATUS THEREFOR Filed May 15. 1952 2 Sheets-Sheet 2 NUIvlll'l'l Ill llv'llll l.

IN V EN TOR. JW 7% BY WK,M

United States Patent O METHOD OF COMBUSTION FOR LOW-GRADE FUEL ANDAPPARATUS THEREFOR Townsend Tinker, Orchard Park, N.Y., assignor, bymesne assignments, to American Radiator & Standard Sanitary Corporation,New York, N.Y., a corporation of Delaware Application May 15, 1952,Serial No. 287,889

4 Claims. (Cl- 158-7) This invention relates to new and usefulimprovements in methods of combustion for very low-grade fuels andcombustion apparatus therefor and more particularly to a method ofcombustion and apparatus for the burning of a. very lean mixture of Cand other inert gases such as N, and C0,.

The general object of this invention is to provide a novel method ofcombustion and apparatus therefor for burning and reclaiming waste heatfrom the exhaust gases from an iron melting cupola. The reclaimed wasteheat from cupola exhaust gases may be used to heat the incoming blastair for the cupola or for any other suitable heating purposes.

The conditions required to burn satisfactorily cupola exhaust gases arequite different from those required for the combustion of richer fuelgases. The exhaust gases from an iron melting cupola consist of amixture of inert gases such as N, and CO, and a small percentage ofcombustible CO. The N, present in these exhaust gases originates withthe combustion air in the cupola while the C0, is produced from completecombustion of the coke in the cupola and the CO is produced byincomplete combustion of a part of the coke. The CO is the only burnableingredient in the cupola exhaust gases and is normally'present only toan extent of about 12 to 18%. The combustible heat content per cubicfoot of cupola gas amounts to only about 50 B.t.u. as compared with 1000B.t.u. for natural gas and 500 B.t.u. for manufactured gas. As a resultof the very small quantity of combustible CO in the cupola gases, thecombustion of the CO in the presence of air or 0 takes place with a verylazy flame which propagates-very slowly through the mixture. In spite ofthe very low heating value of these gases, there is such a quantity ofgas produced in cupola operation that if it were all completely burned,the heat quantity would be more than enough required to furnish heat forthe cupola blast air and could provide heat for other purposes.

It, therefore, becomes necessary at times to burn only a relativelysmall portion of the very lean cupola gases which introduces problems inthe burning process. For example, if enough air is brought into thecupola gases to burn one-third of the CO'present, and if this airquantity were thoroughly mixed with the entire exhaust gas stream, theresultant diluted gas stream would have such a small percentage of 0,present that it would be non-inflammable and could not be made to burnsatisfactorily. On the other hand, if the air is introduced in a largelow velocity stream so as to remain as an air stream traveling alongwith the cupola exhaust gas stream and not be instantaneously mixed orcompletely diluted into the gas stream, then there is a slow mixingprocess or dilfusion of air into the gas and of gas into the air. Thisdiifusion of air and gas establishes a boundary layer around the airstream wherein there is a sufliciently rich mixture of CO and O, tosupport combustion. It is, therefore, possible to establish burningconditions on the boundary layers of the large low velocity air streams.

The initial combustion which takes place along the airgas boundary layerreleases heat which raises the temperature of the air and cupola exhaustgases traveling through the combustion chamber. As the combustiontemperature increases, the burning process can be carried on with lower0 concentrations than could be ignited in the lower temperature regionsbefore the additional heat of combustion had been released.

If nothing further were done than to introduce large streams of air, theboundary layer mixing and burning process would take place relativelyslowly and the flames would continue for a very long distance requiringan extremely long combustion chamber to obtain a complete combustionwith all of the air introduced. The reason for this very slow rate ofcombustion seems to be a result of the very slow rate at which the airdiffuses into the cupola exhaust gas stream. The present apparatus andmethod of combustion provide for a more complete and more rapidcombustion in a smaller combustion chamber than has been previouslypossible when burning such lean gases as are generated by an ironmelting cupola.

This invention comprises a new and improved method of combustion and anew and improved apparatus for effecting said method of combustion whichwill be described more fully hereinafter and the novelty of which willbe particularly pointed out and distinctly claimed.

In the accompanying drawings to be taken as a part of thisspecification, there are clearly and fully illustrated two preferredembodiments of this invention, in which drawings:

Figure 1 discloses in more or less diagrammatic form a cupola connectedto a combustion apparatus which is operable to burn cupola exhaust gasesin accordance with the improved method of combustion and which isarranged to supply heat to the incoming blast air for the cupola, and

Fig. 2 discloses an apparatus similar in construction to Fig. 1 whereinthere is provided a controlled by-pass around the combustion chamber.

Referring to the drawings by characters of reference and moreparticularly to Fig. 1, there is shown in more or less diagrammatic forman iron melting cupola 1 having an air inlet bustle 2 and a gas ofi-takebustle 3. The gas off-take bustle 3 is connected by a gas transfer duct4 to the inlet 5 of a vertical cylindrical combustion apparatus 6. Thecombustion apparatus 6 has a hollow cylindrical interior which extendsvertically therethrough and which provides a combustion chamber 7. Thecombustion apparatus 6 is illustrated as being considerably shorter thanits actual construction as indicated by the dotted lines 8. Thecombustion air for burning the cupola exhaust gases in the combustionchamber 7 is supplied by a fan or blower 9 which is connected by a duct10 to an annular air inlet bustle 11. The air inlet bustle 11 isconnected by a plurality of conduits 12 to a plurality of inletconnectors 13, respectively, and having valves 12 controlling flowtherethrough. The air inlet bustle 11 is also connected by a pluralityof conduits 14 to a plurality of air inlet jets 15. The conduits 14 eachhave a control valve 16 therein which may be adjusted to determine thevolume of air flow therethrough and the velocity of the air issuing fromthe jets 15. The combustion chamber 7 is provided with an ignition meanssuch as a gas pilot flame 17 issuing from a pilot burner nozzle 18 at apoint between the large air inlet connections 13 and the air jet inlets15. The pilot burner nozzle 18 is supplied with gas through a supplyconduit indicated by the dotted lines 19. At a point beyond the airinlet jets 15 there may be provided a second pilot flame 20 issuing froma burner nozzle 21 and supplied with gas through a supply pipe indicateddiagrammatically as 22. The pilot flame 20 assists in igniting thecombustible mixture of gas and air after it has passedthe high velocityair jets 15. At the upper end ofthe combustion chamber the combustionproducts pass through aiheat exchanger 23 and are discharged toatmosphere through a stack or fiue 24. The

cupola 1 which provide's'the' exhaustgases whichare" burned'in thecombustionchamber 7 is ,supplied with air by a high pressurefan25vvhichis preferably operable to supply air under a sufficientpressure to cause the same to move througlrthe cupola forcombustionthereinand through the combustion apparatus 6*andout the flue: 24: I Thefan 25 is'connectedby-aconduit26i to one-side"of the heat exchanger 23?The b'last air for the cupola is heated to a desired.temperatureirrtheheatexchanger 23 and is dischargediinto theintakebustle 2 ofiithe cupola" 1 through a conduit'27. The airsuppliedtothecombus tion apparatus 6",is"controlledby' a'valve or'dampcr28 in the supplyduct lllwhichiizcoritrolled by a control' device 29which is shown diagrammatically and which is controlled by asuitablethermostatic element 30. The" element 30 is 'l'flSPOIiSiVe'iOI' thetemperature of combustion products at the outlet'end of the combustionapparatus 6 after said'products have passedgthroughtheheat' exchanger23; or may be positioned at3fl for response to air temperature attheoutlet from the heatexchauger 23;

Operation In operation, this apparatus and cornbustionmethod functiongenerally as-follows: When thehot blast air is supplied through conduit27 'andintake bi1stle 2 to the cupola-1 and the chargetherein isignited; thecombustion products which are dischargedffom; the cupolacomprise about 12 to 18% CO and 82to-88% CO and N The-cupola exhaustgases are-removed through the off-take bustle 3 and discharged throughthe supply duct 4 to theinlet 5 of thecornbustiorr apparatus 6.

As the exhaust gases move upward within-thecombustion' chamber 7, theyfirst pass the main air inlet 13; At this point a relatively largequantity of air is introduced into that the flame iswell establish'ed;i.e;, where, the rate of' difiusion of gas and air and thc'rate'ofcombustion have become fairly rapid, the gaseswill havereached theposition of'the supplemental'aininlets or high' velocity jets 15. Atthis point, anadditional amountof required to complete the combustion ofthe desired amount of CO in the exhaust gases'is introducedin'aplurality of high velocity air jets intersecting the gas and air streamswhich causes a'very high" turbulencein the gas and air-stream and arapid diffusion of the gas into the air stream and air; into the gasstreamto increase very rapidly the rate of combustion. By the use ofthese supplemental high velocity air jets, it is possible to obtainsubstantially complete combustion of the cupola exhaust gases ina-relatively small combustion chamber. The supplemental pilotfiame20may. be providedfto -assist in the spreadof combustion throughthe mixture after it has passed the air jets to insure thatno burnablemixture passes thatpoint' in, the. combustion chamber. The combustionproducts pass through the heat exchanger 23 and give up a large portionof'ith'eir heatto th'e'blast air which is supplied the fan'25 and arethen discharged through the outlet flue-orstackM-Q Since in an-apparatusof this typeonly' a ;portion ofthe COis burned at any particulartime;then-temperature of the combustion products can be controlled bycontrolling the total amountof combustion which takes place which" isaccomplished by varying the quantity of air supplied through the mainair inlets 13 and the air jets 15. This temperature control is effectedby a thermostatic control mechanism comprising a goontrqller 29 andthermostatic element 39 which is positioned for response to outlettemperattn'enffom the:combustion" chamber 7 onou'tlet temperaturefrom'the heat'exchanger 23. This thermostatic: comrol isiefiectivegto'vary the extentlofiopeningg of adampenZS'ttodetermine the quantityofair supplied to the combustion chamberfl; It*should 'also:-b'enoted thatthe control which is elfective through movement of the damper28tcould1also-be eflected by varying the speed of the fan 91' When onlyapart of the cupola gases is being burnedi the whichds' mixed therewithwill cause a complete combustion of only that part. The resultingcombustion products will thereupon be thoroughlv'mixed' with" theunburned" gas portion to produce the controlled outlet temperature for'heating the heat" exchanger and the air passing therethrough toits'djesiled value.

In the apparatus which is shown inFig. 2'; every element of constructionis the same as in Fig; 1i and" is given the same reference numeral as inFig. 1; except for the addition of a: by -pass around the combustionchamber and a dampen control mechanism therefon In this constructionthere'is provided 'a b'y-pass conduit, 4 from the inlet-Sof thecombustion apparatusfi to the'outlet end portion of said apparatus.'Iheby-pass conduit 4 is provided with a valve or damper-"31- which iscontrolled byfa control mechanism 32"opjerated in response" to athermostatic controller, 33 which"mayfjre'- spond to combustion" outlettemperature"or' heafexchangeroutlet "temperature. The byj-passiconduif lis connected to the outlet end of combustion 'chamberfland dischargesthereinto at} a, point 'just belowuhjefheat exchanger 23; In thisarrangement, the controller 29,3. is preferably a combustion responsivecontrollefhaving i its element 301responsive to the state'ofcombustionjjust' ahead of the by-pass inlet 34. I p

In thistorm of apparatus and'methodf'ofcombustion; theportion of cupolaexhaust gas 'which passes1h1 TOi-1ghfl the combustion chamber 7 isburned inithegsamemanner as indicated in Fig 1. However, in thisarrangement; alI oftthe 'gas which'passes through thecornbustionjfchamber 7 is completely,burned and so'much of the gas asisflnot required to be burned is by-passed' throughftheby j-pass conduit4 and mixed' With the eombustionproductsiust'; prior to entering theheat exchanger '23- to' obtain'the desired temperature; The relativeamount oficupola, exhaust gases which pass through thejcombustionchain-. her 7 and through the by-pass, conduit 4% arecontrolled'; by avalveor'damper 3l which'isoperated by a controlle 32 having athermostatic element 33 positioned: for response to temperature on theoutlet side of, theth'eat exchanger 23. Theair supply-damper28is1automatically, controlled for complete combustion of;the gases.fiowin g through the combustionchamber 7.' t,

Although in this specification there havebeen described only twoembodiments of the method of combustion which embodies this inventionand, the app ratus for? accomplishing that method, it'fwill' beobvious,to those; skilled in the art that other modificationsof-thismethod, and other apparatus for accomplishing thism'ethodlmightbeconstructedwithout departingfrom', the scope, and, intent of thisinvention which should'be limitedionly, by; the appended" claims.

Having thus described'the'invention, what is; and desired to besecuredb'y'Letters Patent of the Unitedt Statesis:

l.- The process ofiburning, a movinggas"streamjcomji prising a very leanmixture of and inert gasesj' suiclrj as N and'Coiwhichmomprisesthejstepsjof di (iii-lg "v the streaminto'separate-parts, introducing fa; quant ty ot-j air sufiicient forcomplete combustion of one gas stream part, igniting the gas-airmixture, and mixing the combustion products of said one gas stream partwith the other gas stream part subsequent to said combustion to obtain apredetermined temperature.

2. The process of burning a moving gas stream comprising a very leanmixture of CO and inert gases such as N, and CO which comprises thesteps of dividing the stream into separate parts, introducing a part ofthe air required for complete combustion of one gas stream part,igniting the gas-air mixture, introducing the balance of the requiredcombustion air in a plurality of high velocity jets at a point in thegas stream at which combustion temperature has reached a valuesufiicient to effect a rapid difiusion of air into the combustiblemixture, and mixing the combustion products of said one gas stream partwith the other gas stream part subsequent to said combustion to obtain apredetermined temperature.

3. A combustion apparatus for burning a very lean mixture of CO andinert gases such as N; and C0 comprising means forming a hollowcombustion chamber having an inlet and an outlet for said gas mixture,means including a plurality of large air supply conduits for supplying aquantity of combustion air at low velocity to the inlet end of saidcombustion chamber, means including a plurality of high velocity airinlet jets opening into said combustion chamber and spaced from said airsupply conduits in the direction of the outlet end of said combustionchamber, ignition means in said combustion chamber at a point betweensaid air supply conduits and said air inlet jets, a by-pass conduit fromthe inlet to the outlet end of the combustion chamber, valve meanscontrolling the relative flow of gas through said combustion chamber andsaid by-pass conduit, and thermostatic means controlling said valvemeans in response to the heat output of combustion products at theoutlet end of said combustion chamber.

4. A combustion apparatus for burning a very lean mixture of CO andinert gases such as N: and CO comprising means forming a hollowcombustion chamber having an inlet and an outlet for said gas mixture,means including a plurality of large air supply conduits for supplying aquantity of combustion air at low velocity to the inlet end of saidcombustion chamber, means including a plurality of high velocity airinlet jets opening into said combustion chamber and spaced from said airsupply conduits in the direction of the outlet end of said combustionchamber, ignition means in said combustion chamber at a point betweensaid air supply conduits and said air inlet jets, a bypass conduit fromthe inlet to the outlet end of the combustion chamber, valve meanscontrolling the relative flow of gas through said combustion chamber andsaid by-pass conduit, thermostatic means controlling said valve means inresponse to the heat output of combustion products at the outlet end ofsaid combustion chamber, and an automatically controlled air supplyvalve operated by a control device responsive to the state of oxidationof combustion products and operable to vary the air supply to insurecomplete combustion of the gas stream portion flowing through thecombustion chamber.

References Cited in the file of this patent UNITED STATES PATENTS1,262,841 Randolph Apr. 16, 1918 1,627,536 Vial et al May 3, 19271,659,869 Gow Feb. 21, 1928 1,950,787 Ellingham Mar. 13, 1934 2,110,209Engels Mar. 8, 1938 2,203,554 Uhri et al, June 4, 1940 2,253,920 VaughanAug. 26, 1941 2,282,551 Yates May 12, 1942 2,368,827 Hanson et al. Feb.6, 1945

3. A COMBUSTION APPARATUS FOR BURNING A VERY LEAN MIXTURE OF CO ANDINSERT GASES SUCH AS N2 AND CO2 COMPRISING MEANS FORMING A HOLLOWCOMBUSTION CHAMBER HAVING AN INLET AND AN OUTLET FOR SAID GAS MIXTURE,MEANS INCLUDING A PLURALITY OF LARGE AIR SUPPLY CONDUITS FOR SUPPLYING AQUANTITY OF COMBUSTION AIR AT LOW VELOCITY TO THE INLET END OF SAIDCOMBUSTION CHAMBER, MEANS INCLUDING A PLURALITY OF HIGH VELOCITY AIRINLET JETS OPENING INTO SAID COMBUSTION CHAMBER AND SPACED FROM SAID AIRSUPPLY CONDUITS IN THE DIRECTION OF THE OUTLET END OF SAID COMBUSTIONCHAMBER, IGNITION MEANS IN SAID COMBUSTION CHAMBER AT A POINT BETWEENSAID AIR SUPPLY CONDUITS AND SAID AIR INLET JETS, A BY-PASS CONDUIT FROMTHE INLET TO THE OUTLET END OF THE COMBUSTION CHAMBER, VALVE MEANSCONTROLLING THE RELATIVE FLOW OF GAS THROUGH SAID COMBUSTION